Historically, complete removal of a disc from between adjacent vertebrae resulted in fusing the adjacent vertebrae together. This “spinal fusion” procedure, which is still in use today, is a widely accepted surgical treatment for symptomatic lumbar and cervical degenerative disc disease. More recently, disc arthoplasty may be utilized to insert an artificial intervertebral disc implant into the intervertebral space between adjacent vertebrae. Such a disc implant allows limited universal movement of the adjacent vertebrae with respect to each other. The aim of total disc replacement is to remove pain generation (caused by a degenerated disc), restore anatomy (disc height), and maintain mobility in the functional spinal unit so that the spine remains in an adapted sagittal balance. Sagittal balance is defined as the equilibrium of the trunk with the legs and pelvis to maintain harmonious sagittal curves and thus the damping effect of the spine. In contrast with fusion techniques, total disc replacement preserves mobility in the motion segment.
One such intervertebral implant includes an upper part mounted to an adjacent vertebra, a lower part mounted to another adjacent vertebra, and an insert located between these two parts. An example of such a total disc replacement intervertebral implant is shown in U.S. Pat. No. 6,936,071, titled “Intervertebral Implant”, the contents of which are incorporated herein by reference in their entirety. To provide an anchor to mount the upper and lower parts to the adjacent vertebrae, each part includes a vertically extending keel. While this and other known implants represent improvements in the art of artificial intervertebral implants, there exists a continuing need for improvements of these types of implants.